Non-aqueous heat transfer fluid and use thereof

ABSTRACT

A non-aqueous, reduced toxicity polyhydric alcohol based heat transfer fluid is provided comprised of at least one polyhydric alcohol that acts as an ADH enzyme inhibitor, such as for example propylene glycol, thereby reducing the toxicity of ethylene glycol if ethylene glycol. The heat transfer fluid may also include corrosion inhibitors that are soluble in the polyhydric alcohols used for the heat transfer fluid. The heat transfer fluid may be used as a coolant in internal combustion engines such as automobile engines, a coolant for cooling electrical or electronic components, as a heat transfer fluid for solar energy heating systems, or a heat transfer fluid for maintaining temperatures in industrial processes. A low toxicity preparation fluid for absorbing water from heat exchange systems prior to installation of the heat transfer fluid is also provided that is comprised of ethylene glycol and at least one polyhydric alcohol, preferably propylene glycol, that acts as an ADH enzyme inhibitor.

RELATED APPLICATIONS

[0001] The present application is a continuation-in-part of patentapplication U.S. Ser. No. 09/910,497 filed on Jul. 19, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a substantiallynon-aqueous, reduced toxicity heat transfer fluid for use in heatexchange systems such as a coolant for internal combustion engines, acoolant for electrical or electronic components, a heat transfer fluidfor solar energy heating systems, or a heat transfer fluid formaintaining temperatures in industrial processes. The present inventionalso relates to a compatible reduced toxicity preparation fluid forabsorbing residual water from heat exchange systems in preparation forinstalling the non-aqueous heat transfer fluid.

BACKGROUND OF THE INVENTION

[0003] Heat transfer fluids are used in a variety of applications. Onecommon use of heat transfer fluids is as a coolant in internalcombustion engines. Most heat transfer fluids that are currently usedcontain water mixed with ethylene glycol (EG), a hazardous substancethat can cause environmental contamination as a result of improperdisposal. These fluids can cause dangerous health effects upon humansand other mammals if they are ingested. In addition, adverse healtheffects can occur due to exposure to used heat transfer fluids as aresult of contamination by elemental heavy metal precipitates and toxicinhibitors that are added to prevent water related reactions.

[0004] Every year nearly 700 million gallons of heat transfer fluidconcentrates are sold in the United States alone, and about 1.2 billiongallons are sold worldwide. Concentrates are formulations to which asubstantial water fraction is added to form the actual heat transferfluid. Much of the heat transfer fluid made from these concentratesreplaces similar but spent heat transfer fluid drained from heattransfer systems such as automobile engine cooling systems. It isestimated that a significant percentage of the concentrates are disposedof improperly, resulting in contamination of the environment. Improperdisposal by consumers is a major cause of this environmentalcontamination. Another major source of environmental contamination isleakage, spills and overflows from heavy duty vehicles. Experience withheavy duty vehicles shows that it is common to lose 10% of the engineheat transfer fluid volume after every 12,000 to 18,000 miles ofoperation due to leaks in the system components, such as the water pump,hose clamps or radiator core. This rate of loss is equal to about onegallon/month for the typical highway truck, which is the equivalent of aleakage rate of one drop per minute. A heat transfer fluid leak rate ofone drop per minute is likely to go unnoticed, but can in total add upto a significant loss.

[0005] In some operations using heavy duty vehicles, overflows accountfor far more heat transfer fluid loss than low level leaks at the waterpump, hose clamps or radiator core. Overflows occur due to overheatingor when an engine cooling system is overfilled. When an engine coolingsystem is overfilled, operation of the engine heats the heat transferfluid, causing expansion of the fluid that cannot be contained in thesystem. Pressure relief valve lines typically allow excess fluid toescape to the ground. Small spills and leaks (less than a gallon) ofheat transfer fluid eventually will biodegrade with little impact to theenvironment. However, before biodegradation occurs, these spills andleaks can present a toxic danger to pets and wildlife.

[0006] Current engine coolant formulations typically utilize water asthe primary heat removal fluid. The water content of an engine coolantis typically 30% to 70% by volume, depending upon the severity of thewinter climate. The second major component of a conventional enginecoolant is a freeze point depressant. The freeze point depressant mostfrequently used is EG, which is added to water in a range from 30% to70% by volume of the engine coolant to prevent freezing of the waterduring winter. EG is a polyhydric alcohol, an alcohol with more than onehydroxyl (OH) group. Many polyhydric alcohols (such as, for example,diethylene glycol, triethylene glycol, tetraethylene glycol, propyleneglycol, diapropylene glycol and hexylene glycol) when added to waterdepress the freezing point of the water and elevate the boiling point ofthe water. The most commonly used polyhydric alcohol in engine coolantformulations is EG because it has excellent characteristics for thatpurpose and because it is the least expensive of the polyhydricalcohols.

[0007] In addition to water and EG, an additive package containingseveral different chemicals is included. These additives are designed toprevent corrosion, cavitation, deposit formation and foaming, and areeach present usually in concentrations of from 0.1% to 3% by weight ofthe coolant concentrate. The additives are typically mixed with thefreeze point depressant to form an antifreeze concentrate, which can beblended with water to form the engine coolant. As an alternative to EG,a formulation composed of the polyhydric alcohol propylene glycol (PG)with additives has been used as a freeze point depressant, primarily dueto PG's lower toxicity rating as compared to EG.

[0008] The same coolant formulations are not used for all enginesbecause different engine types have different requirements. For example,heavy-duty engines require a high concentration of sodium nitrite as anadditive to control iron erosion of cylinder liners due to cavitation.Cylinder liner cavitation can occur when a substantial portion of theengine coolant is made up of water. When, for example, a mixture of 50%water and 50% EG is used (50/50 EG/W) in a heavy duty engine, theoperating temperature of the coolant (about 200° F., 93.3° C.) is fairlyclose to the boiling point of the coolant (about 250° F., 121.1° C. at10 psig). Vibration of the cylinder liner creates a low pressure areaduring the part of the cycle when the liner moves away from the coolantand a high pressure area when the liner moves toward the coolant. Duringthe low-pressure part of the cycle coolant becomes vaporized, only toimmediately collapse back to liquid during the high pressure part of thevibration cycle. The repeated high frequency formation and collapse ofcoolant vapor attacks the surface of the liner, eroding small amounts ofiron. Sodium nitrite is added to limit the amount of vapor impacting thecylinder wall. By comparison, the use of sodium nitrite is not necessaryor desirable in light duty engines. The complexity of balancing variouswater to EG (or PG) ratios and different additive formulations canresult in improper freeze protection and clogged radiators and heatercores when the engine coolant is misformulated. As discussed furtherbelow, many of these problems are a result of the need for a substantialwater fraction in these engine coolants.

[0009] Another difference between heavy-duty engines and light dutyautomobile engines is the use of supplemental coolant additives in heavyduty engines to replenish additives that are depleted with service.Supplemental coolant additives are not used or required in passengercars that have a coolant life of 20,000 miles (32,186 km) to 30,000miles (48,279 km). Heavy-duty service usually demands 200,000 miles(321,860 km) to 300,000 miles (482,790 km) before coolant replacement.The longer coolant service requirement results in the need toperiodically replenish the inhibitors in heavy-duty engine coolants.Examples of commonly used supplemental coolant additives include sodiumnitrite, dipotassium phosphate, sodium molybdate dihydrate, andphosphoric acid.

[0010] Supplemental coolant additives must be chemically balanced withthe coolant volume, which can be difficult and costly to controlproperly. Improper balancing of additives can result in severe damage tocooling system components and the engine. If the concentration of thesupplemental coolant additives in the coolant is too low, corrosion andcavitation damage to the engine and cooling system components can occur.If, on the other hand, the concentration of supplemental additives istoo high, additives can precipitate from the coolant solution and clogradiator and heater cores. A further concern with supplemental coolantadditives is that they may, under certain conditions, be difficult toproperly dissolve in the engine coolant. If the supplemental additivesdo not completely dissolve, they may be a source of additional cloggingproblems in the engine.

[0011] Glycols make up 95% by weight of conventional antifreeze/coolantconcentrates, and after blending with water, about 30% to 70% by volumeof the coolant used in the vehicle. Because of its relative abundanceand lower cost as compared with alternative glycols, conventionalantifreezes are almost always formulated with EG. A major disadvantageof using EG as a freezing point depressant for engine coolants is itshigh toxicity to humans and other mammals if ingested. Toxicity isgenerally measured in accordance with a rating system known as the LD₅₀rating system, which is the amount of a substance expressed inmilligrams per kilogram of body mass that, when fed to laboratory ratsin a single dose, will cause the death of 50 percent of the laboratoryrats. A lower LD₅₀ value indicates a higher toxicity (i.e., smalleramounts of the substance can be lethal). An LD₅₀ value of less than orequal to 5,000 milligrams per kilogram of body mass (mg/kg) can classifyan antifreeze concentrate as hazardous. Because EG has an LD₅₀ value of4,700 mg/kg, EG is considered hazardous by this rating system. Moreover,EG is a known toxin to humans at relatively low levels.

[0012] The toxicity associated with EG is caused by the metabolites ofEG, some of which are toxic. EG, when ingested, is metabolized by thealcohol dehydrogenase enzyme (ADH), converting it to glycoaldehyde.Glycoaldehyde further metabolizes to glycolic acid (glycolate). Theaccumulation of glycolic acid causes metabolic acidosis. Also, glycolicacid accumulation correlates with a decrease in arterial bicarbonateconcentration. Some of the glycolic acid metabolizes to glyoxylic acid(glyoxylate), which further metabolizes to oxalic acid (oxylate). Oxalicacid binds to serum calcium in the bloodstream, and precipitates ascrystals of calcium oxalate.

[0013] Characteristic symptoms observed with EG ingestion include aniongap metabolic acidosis, hypocalcemia, cardiac failure, and acuteoliguric renal failure. Calcium oxylate crystals in many cases can befound throughout the body. Calcium oxylate crystals in the kidneys causeor are associated with the development of acute renal failure.

[0014] As reported in Toxic Release Inventory Reporting; Notice ofReceipt of Petition, Federal Register, Vol. 63, No. 27, Feb. 10, 1998,the lethal dose of EG for a human is approximately 1,570 mg/kg bodymass. Consequently, EG is classified by many regulatory authorities as adangerous material. EG also has the added complication of a sweet smelland taste thereby creating an attraction for animals and children.

[0015] Due to the toxicity of EG, in recent years a base fluidconcentrate with about 95% PG and additives has been used as asubstitute for EG with additives in many antifreeze formulations. PG hasan LD₅₀ value of 20,000 mg/kg as compared to EG's 4,700 mg/kg. PG isconsidered essentially non-toxic, and it has been approved by the U.S.Food and Drug Administration as a food additive. One impediment to morewidespread usage of PG as a base fluid for antifreeze concentrates isits relatively high cost as compared to EG.

[0016] All conventional antifreeze concentrates, whether EG or PG based,contain water in their formulations. EG antifreeze concentrates requirea small percentage of water in their formulation because EG, by itselfand without any water, freezes at +7.7° F. (−13.5° C.). A small amountof water must be added to depress the freezing point. Addition of fourpercent water by volume to EG lowers the freezing point of the mixtureto 3° F. (˜19.4° C.). The freezing point of PG (by itself and withoutwater) is relatively low, −76° F. (−60° C.). However, because some ofthe required additives are not readily soluble in either EG or PG, wateris added to all conventional concentrate mixtures. Three to five percentby weight water is typically included in coolant concentrates todissolve certain additives that will not dissolve in glycols. Addedwater is essential in conventional concentrates to keep the additivesdissolved, particularly as the concentrates may be stored for extendedperiods.

[0017] Although three to five percent water is intentionally added to EGand PG concentrates to dissolve water soluble additives, addition ofwater alone is not effective over long periods of time to maintain theadditives in solution. For long term storage, conventional coolantconcentrates must be agitated periodically in order to keep theadditives in solution until blending of the concentrate with water tomake the final coolant mixture. If stored too long as a concentrate(over 6-8 months), one or more of the additives may precipitate from thesolution and accumulate in the bottom of the container, forming a gel.The gelled additives will not return to solution, even with agitation.Even when mixed with water in an engine coolant, for example as 50/50EG/water, the water soluble additives can form a gel if not agitatedregularly by running the engine. This can be a severe problem forengines used in stationary emergency pumps and generators as well asmilitary and other limited use engines.

[0018] The water added to concentrates to form an engine coolant canalso cause formation of potentially hazardous products. Water atelevated temperatures can be highly reactive with the metal surfaces ina cooling system. The water can react with lead and copper materialsfrom radiators, including brass and lead solder. As a result,precipitates of heavy metals, such as lead and copper, can becomesuspended in the circulating coolant in the engine. Water is also highlyreactive with light alloys, such as aluminum, and the water fraction ofthe coolant can generate large amounts of aluminum precipitates,particularly at higher coolant temperatures. Even with the addition ofadditives to control these reactions, aluminum is constantly lost to theconventional engine coolants containing approximately 50/50 mixtures ofEG and water.

[0019] Corrosion of metal surfaces in engine cooling systems usingconventional glycol/water coolants is also caused by the formation oforganic acids in the coolant, such as pyruvic acid, lactic acid, formicacid, and acetic acid. Polyhydric alcohols, such as EG or PG, in aqueoussolutions can produce acidic oxidation products when in the presence ofhot metal surfaces, oxygen from either entrapped air or water, vigorousaeration, and metal ions which catalyze the oxidation process. Moreover,formation of lactic acid and acetic acid is accelerated in coolantsolutions at 200° F. (93.3° C.) or above while in the presence ofcopper. Formation of acetic acid is further accelerated in the presenceof aluminum in coolant solutions at 200° F. (93.3° C.) or above. Theseacids can lower the pH of the coolant. Among the metals and alloys foundin engine cooling systems, iron and steel are the most reactive tosolutions containing organic acids, whereas light metals and alloys,such as aluminum, are considerably less reactive.

[0020] To counteract the effect of organic acids, conventional EG or PGbased concentrates include buffers in their formulations. The buffersact to maintain the pH of the engine coolant in the range ofapproximately 10 to 11 as organic acids are formed. Some examples oftypically utilized buffers include sodium tetraborate, sodiumtetraborate decahydrate, sodium benzoate, phosphoric acid and sodiummercaptobenzothiazole. These buffers also require water in order toenter into and remain in solution. As the buffers in the coolantsolution become depleted over time, the water fraction of the coolantreacts with the heat, air and metals of the engine, and, as a result,the pH decreases because of the acids that form.

[0021] In addition to buffers, all currently used and previously knownengine coolants require inhibitors to control the corrosive effects fromthe water content of the coolant. The inhibitors must be balanced toavoid interactions with each other that would decrease their individualeffectiveness. For example, phosphates and borates can decrease thecorrosion protection provided to aluminum by silicates. Moreover, theinhibitors must not be used in excess concentration (in an attempt toextend the depletion time) because that can cause damage to systemcomponents due to precipitation resulting in plugging of radiator andheater core tubes. In addition, silicates, silicones, borates andphosphates are chemically abrasive and can erode heat exchanger tubesand pump impellers. Nevertheless, the inhibitors must still exist in aconcentration adequate for protecting all of the metals.

[0022] All currently used coolant formulations require the addition ofwater to solubilize additives used as buffers, corrosion inhibitors andanti-foam agents. In addition, these water soluble additives requireheat, extreme agitation, and extensive time for the water to react andcause the additives to dissolve. These requirements add significant costand complexity to the formulation and packaging of antifreezeconcentrates. The energy costs and time required for blending, beforepackaging, are a major factor in the processing costs. Also, becausemany of these additives may interfere with each other and cause anincomplete solution and failure of the formulation process, theformulating process must be monitored constantly to assure a properblend.

[0023] Thus, the additive package that is included in known coolantconcentrate formulations can consist of from 5 to 15, and typically from8 to 15, different chemicals. These additives are broken down into majorand minor categories, depending upon the amount used in an enginecoolant formulation: MAJOR (0.05% to 3.0%) MINOR (<0.05%) BufferDefoamer Corrosion inhibitors Dye Cavitation inhibitors Scale inhibitorSurfactant Chelates

[0024] In addition, some of the additives themselves, e.g., borates,phosphates, and nitrites, are considered toxic. Thus, not only do allknown coolant concentrate formulations include additives that requireheat, extreme agitation and extensive time for the water to react andcause the additives to dissolve, but the additives themselves aresometimes toxic. Further, the additives require complex balancing whichaccommodates the prevention of interference between the additives, whilealso preventing the excessive presence of any one additive in thecoolant.

[0025] The applicant has a co-pending application U.S. Ser. No.08/991,155 filed on Dec. 17, 1997, which is continuation-in-part ofpatent application U.S. Ser. No. 08/409,026 filed on Mar. 23, 1995, thecontents of each of which are expressly incorporated herein byreference.

[0026] Accordingly, it is an object of the present invention to overcomeone or more of the drawbacks and disadvantages of the prior art andprovide a reduced toxicity, non-aqueous heat transfer fluid.

SUMMARY OF THE INVENTION

[0027] The present invention relates to a heat transfer fluid that usespolyhydric alcohols, preferably propylene glycol (PG) or a mixture of(PG and EG), as its base fluid without the addition of water and istherefore termed non-aqueous. The use of water in the non-aqueous heattransfer fluid is not required as a means to dissolve additives becausethe only additives used are corrosion inhibitors that are soluble inneat PG and EG. By avoiding corrosion inhibitors that require water fordissolution, the formulation of the present invention is easier to blendand requires much less time to blend, thereby lowering blending costs.The instant invention, of a water-free polyhydric alcohol-based heattransfer fluid (preferably PG or PG with EG), utilizes a uniqueformulating process which results in a fully-formulated and stabilized,non-aqueous heat transfer fluid suitable for use as an engine coolant.

[0028] In a second aspect of the present invention, EG based non-aqueousheat transfer fluids are provided that are non-toxic. The inventors havediscovered that PG acts as an ADH enzyme inhibitor, slowing orpreventing the metabolism of EG into the toxic metabolites related withEG poisoning, and that when PG is mixed with EG, the resulting mixtureis essentially non-toxic even up to EG proportions of 99 percent byweight. The inventors have discovered that the polyhydric alcoholglycerol also acts as an ADH enzyme inhibitor, and that when glycerol ismixed with EG the resulting mixture is likewise essentially non-toxic.

[0029] One advantage of the present invention is that all resultingnon-aqueous heat transfer -fluids are suitable for use as enginecoolants in ambient temperatures up to 130° F. (54.4° C.) or hotter and,depending on the selection of the polyhydric alcohols, a non-aqueousheat transfer fluid can be blended for use as an engine coolant inambient temperatures as cold as −76° F. (−60° C.).

[0030] Another advantage of the present invention is that, when thenon-aqueous heat transfer fluid is used in a cooling systems such asthose disclosed in U.S. Pat. Nos. 4,550,694; 5,031,579; 5,381,762;5,385,123; 5,419,287; 5,868,105 and 6,053,132, and even in coolingsystems designed for use with water-based coolants, the cooling systemcan operate at a significantly lower pressure, thereby reducing stresson engine system components. The lubricous nature of the non-aqueouscoolant of the present invention is benign to rubber, and allows thepump seals, hoses and system components to normally last 150,000 miles(241,395 km) or more, which dramatically lowers the loss of coolant tothe environment because of leaks, while also decreasing overheating.

[0031] A further advantage of the present invention is that thecorrosion inhibitor additives will remain dissolved, without agitation,for many years of storage. Another advantage is that non-aqueouscoolants according to this invention will not cause cylinder linercavitation and therefore there is no need for separate formulations forheavy-duty engines. Sodium nitrite, for example, does not need to beadded to provide protection from cylinder liner cavitation erosion.

[0032] Yet another advantage of the present invention is that the lackof water in the fully-formulated non-aqueous heat transfer fluidsaccording to this invention substantially reduces, and in most instanceseliminates, the problem of contamination from precipitates of heavymetals, such as lead and copper. Also, because pH (acidity) is not aconcern with the non-aqueous formulated coolant of the present inventionthere is no need for additives such as borates and phosphates.

[0033] Another advantage of the present invention is that theessentially water-free nature of the coolant formulation eliminatesother water, air, heat and metal-based reactions and eliminates the needfor additives to control these reactions. The reactions and additivesthat are eliminated include:

[0034] 1. Anti-foam reactions/Silicones and polyglycol additives,

[0035] 2. Aluminum corrosion/Silicates,

[0036] 3. Cavitation corrosion/Nitrites,

[0037] 4. Scale inhibitors/Polyacrylates, and

[0038] 5. Anti-fouling/Detergents.

[0039] Another advantage of the present invention is the creation ofnon-aqueous, low-toxicity heat transfer fluids that are suitable for usein heat exchange systems for the cooling of electrical or electroniccomponents. Yet another advantage of the present invention is thecreation of non-aqueous, low-toxicity heat transfer fluids that aresuitable for use in heat exchange systems for the conversion of solarenergy to usable heat. When using the low-toxicity heat transfer fluidsof the present invention in a solar energy conversion application, useof heat exchangers with special double walls, to prevent contaminationfrom the heat transfer fluid, is not required.

[0040] The non-aqueous heat transfer fluid of the present invention maybe prepared by two different methods. In a first method, the additivesare mixed with and dissolved in a quantity of the polyhydric alcoholbase fluid, such as PG or PG and EG, to form an additive/base fluidconcentrate. After complete solution of the additives is achieved, theconcentrated solution is blended into the bulk tank which is filled withindustrial grade PG or PG and EG. In a second method, the additives areintroduced in powder form directly into the bulk blending tank, which isfilled with industrial grade PG or PG and EG. Either of these methods iseasier and less costly than the methods presently used to mix heattransfer concentrates for use in engines with water.

[0041] The present invention also provides for a compatible reducedtoxicity preparation fluid for absorbing residual water from heatexchange systems in preparation for installing the non-aqueous heattransfer fluid. The preparation fluid is comprised of EG and PG, with EGbeing the major fraction and the PG acting as an ADH enzyme inhibitor.The preparation fluid is particularly useful when a previous water-basedheat transfer fluid is being replaced with a heat transfer fluid of thepresent invention.

[0042] Other advantages of the compositions and methods of the presentinvention will become more readily apparent in view of the accompanyingdetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] So that those having ordinary skill in the art to which thesubject invention appertains will more readily understand the subjectinvention, reference may be had to the drawings, wherein:

[0044]FIG. 1 is a graph showing the Freezing Point vs. PG Percentage byweight of PG and EG blends.

[0045]FIG. 2 is a graph showing Predicted LD₅₀ Values for Mixtures ofEthylene Glycol and Propylene Glycol with Corrosion Inhibitors ThatTotal a Constant Concentration of 1.5 Percent (by Weight).

[0046]FIG. 3 is a graph showing Predicted LD₅₀ Values for Mixtures ofEthylene Glycol and Propylene Glycol (by Weight).

[0047]FIG. 4 is a graph showing Predicted LD₅₀ Values for Mixtures ofEthylene Glycol and Glycerol (by Weight).

[0048]FIG. 5 is a graph showing Viscosity vs. Temperature for 100% PGand a 30% PG/70% EG blend by weight.

[0049]FIG. 6 is a graph showing Thermal Conductivity vs. Temperature for100% PG and a 30% PG/70% EG blend by weight.

[0050]FIG. 7 is a graph showing Specific Heat vs. Temperature for 100%PG and a 30% PG/70% EG blend by weight.

[0051]FIG. 8 is a graph showing Density vs. Temperature for 100% PG anda 30% PG/70% EG blend by weight.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0052] The present invention relates to a polyhydric alcohol-basednon-aqueous heat transfer fluid containing additives that areessentially completely soluble in the polyhydric alcohols and that donot require water to dissolve. The polyhydric alcohol fraction of thenon-aqueous heat transfer fluid contains at least one polyhydric alcoholthat acts as an ADH enzyme inhibitor. As used herein and in the claims,the term “acts as an ADH enzyme inhibitor” means that when the substanceis mixed with EG and ingested, the various toxic metabolites of EG thatrelate to EG poisoning do not appear or the production of them issubstantially diminished. EG requires the action of metabolism toproduce the toxic products that result in EG poisoning. The first stepin the metabolism of EG is the conversion of EG to glycoaldehyde,followed by further metabolism that results in highly toxic metabolites.By including a substance that acts as an ADH enzyme inhibitor in theEG-based heat transfer fluid, production of the toxic metabolites of EGcan be reduced or prevented altogether if the heat transfer fluid isingested. The inventors have discovered that both PG and glycerol act asADH enzyme inhibitors.

[0053] Preferably, the polyhydric alcohol fraction is comprised ofeither PG or a mixture of PG and EG. Preferred embodiments of theinvention are described below. The preferred embodiments disclosedherein are to be considered exemplary of the principles of the presentinvention and are not intended to limit the invention to the embodimentsdescribed. Various modifications will be apparent to those skilled inthe art based on the teachings herein without departing from the spiritor scope of the invention disclosed herein.

[0054] In one embodiment of the invention, a mixture of PG and EG isused as the base liquid for the non-aqueous heat transfer fluid. Thenon-aqueous heat transfer fluid may contain EG in any amount rangingbetween 0 percent by weight to about 99 percent by weight of the totalweight of EG and PG in the fluid. In a particularly preferredembodiment, EG comprises about 70 percent by weight and PG comprisesabout 30 percent by weight of the total weight of EG and PG in thefluid. By blending PG and EG in the manner described below, anon-aqueous heat transfer fluid can be produced with desirable physicalproperties for use as an engine coolant in most climates, such asfreezing point, viscosity and specific heat.

[0055] Physical Properties of Mixtures of PG and EG

[0056] PG and EG are very close in chemical structure, and the twofluids will combine to form a homogeneous mixture in virtually anyratio. After they are combined, the fluids remain chemically stable, andneither fluid will separate from the other. The result is a fluid thatwill remain stable as blended, which is important for long-term storage.

[0057] Another advantage of mixing PG and EG in a non-aqueous heattransfer fluid is that, when mixed, EG and PG will evaporate at aboutthe same rate. This is a result of another similar physicalcharacteristic of the two fluids, their vapor pressures. EG has a vaporpressure at 200° F. (93.3° C.) of 10 mm Hg, and PG at the sametemperature has the relatively similar vapor pressure of 16 mm Hg.Accordingly, the two fluids will evaporate at about the same rate. Bycontrast, water has a vapor pressure of 600 mm Hg at 200° F., andtherefore water will evaporate more rapidly than either EG or PG whenexposed to the ambient atmosphere.

[0058] Neat PG freezes at −76° F. (−60° C.) and neat EG freezes at 7.7°F. (−13.5° C.). The freezing point for mixtures of EG and PG rises asthe percentage of EG is increased. In contrast, PG is substantially moreviscous than EG at lower temperatures. However, for mixtures of PG andEG, it was discovered that viscosity at any given temperature decreasedas the percentage of EG increased.

[0059] In a preferred embodiment of the heat transfer fluid containing a30/70 PG/EG mixture, the freezing point is −35° F. (−37.2° C.), which issatisfactory for all but the most severe arctic environments. As shownin FIG. 5, unexpected improvements in the viscosity of the heat transferfluid occur when EG is mixed with PG. The viscosity of the 30/70 PG/EGmixture at −35° F.

[0060] (−37.2° C.) is approximately 1500 centipoise (cp), as compared toa viscosity of approximately 110,000 cp for neat PG at this temperature.In order to accommodate the higher viscosity in embodiments where PGalone is used as the base non-aqueous heat transfer fluid in thecoolant, changes to the size of coolant passages of the system apparatusand to flow rates would likely be necessary. In the embodiment of theinvention comprised of 30/70 PG/EG by weight, the viscosity at lowtemperatures will allow use of the non-aqueous heat transfer fluidwithout changes to coolant passage sizes or flow rates. The 30/70 PG/EGnon-aqueous heat transfer fluid and engine coolant has been tested inengine coolant systems which were cold ambient limited and hadhistorically required radiator, heater core, and pump redesign whenoperating at cold temperatures with 100% non-aqueous PG. The 30/70 PG/EGnon-aqueous fluid was found to operate properly at ambient temperaturesdown to −20° F. (−28.8° C.) without any need for radiator, heater coreor pump redesign.

[0061] Because of the high temperatures that can exist in an engine, theboiling point, thermal conductivity and specific heat of the base liquidis also an important factor in formulating a non-aqueous heat transferfluid for use as an engine coolant. At atmospheric pressure, PG has aboiling point of 369° F. (187.2° C.), which is satisfactory for use asan engine coolant. The boiling point of EG at atmospheric pressure is387° F. (197.3° C.), which is also satisfactory. The acceptable upperlimit for the atmospheric boiling point of a non-aqueous heat transferfluid used as an engine coolant is about 410° F. (about 210° C.). If theatmospheric boiling point is significantly higher than 410° F., thecoolant and critical engine metal temperatures can become too hot. Manypolyhydric alcohols have boiling points that are unacceptably high foruse, by themselves, as non-aqueous coolants. For example, the boilingpoints of diethylene glycol, triethylene glycol and tripropylene glycolare 472.6° F. (244.8° C.), 545.9° F. (285.5° C.) and 514.4° F. (268° C.)respectively. Although these polyhydric alcohols, by themselves, areunacceptable as non-aqueous coolants, any of them may, in lowconcentrations (for example about 10 percent by weight), be combinedwith EG and/or PG to produce a non-aqueous heat transfer fluid with anacceptable boiling point. Preferably, the non-aqueous heat transferfluid of the present invention contains only PG and EG. PG and EGmixtures have boiling points that fall between the boiling points forneat PG and neat EG, all of which are satisfactory for a non-aqueousengine coolant. For example, the preferred 30/70 PG/EG mixture has aboiling point of 375° F. (190.5° C.).

[0062] The polyhydric alcohols that are in the heat transfer fluidformulation must not have boiling points that are too low. Performanceof the fluid depends upon maintaining a substantial temperaturedifference between the operating temperature of the fluid and theboiling point of the fluid (on the order of 100° F., 55.6° C., or more).Also, the boiling point of the polyhydric alcohol that is the ADH enzymeinhibitor should not be too far below the boiling point of EG (387° F.,197.3° C.) such that the vapor pressure of the inhibitor would cause itto evaporate from the mixture. For both of these reasons, the polyhydricalcohols should not have boiling points below about 302° F. (150° C.).

[0063] The thermal conductivity of a non-aqueous heat transfer fluidcomposed of 30/70 PG/EG is also improved over the thermal conductivityof pure PG. FIG. 6 compares the thermal conductivity of 100% non-aqueousPG to the thermal conductivity of a 30/70 PG/EG mixture. As shown inFIG. 6, the 30/70 PG/EG mixture has a thermal conductivity that isapproximately 25% better than the thermal conductivity of 100% PG in theoperating temperature range of 0° F. (−17.8° C.) to 250° F. (121.1° C.).

[0064]FIG. 7 shows that the specific heat of a 30/70 PG/EG mixture isslightly less than the specific heat of 100% PG. This loss is offset asa result of the increased density of the 30/70 PG/EG mixture over 100%PG. As shown in FIG. 8, the density of 30/70 PG/EG mixtures is about 5%greater than the density of 100% PG, and the resultant increase in massof the 30/70 PG/EG blend for a given volume of heat transfer fluid morethan offsets the slight decrease in specific heat.

[0065] Toxicity Testing of EG Combined with PG

[0066] In an unexpected discovery, it was found that the addition of PGto EG resulted in heat transfer fluids that are essentially non-toxic.Limit tests and range tests were conducted in order to estimate thefinal LD₅₀ value of PG/EG mixtures. A limit test establishes whether ornot an LD₅₀ value lies above or below a specific dose. A range test is aseries of limit tests that establishes a range within which an LD₅₀value lies. Before any testing is performed on rats using a mixture ofsubstances that have established LD₅₀ values, a mathematical estimate ofthe LD₅₀ value is performed.

[0067] Ingesting less of a toxic substance decreases its toxic impact.Accordingly, when a mixture of a toxic substance and a non-toxicsubstance is ingested, in which the concentration of the toxic substanceis reduced, more of the mixture must be ingested to produce the sametoxic effect as the pure substance. For example, EG by itself has anacute oral (rat) LD₅₀ value of 4,700 mg/kg. If the EG is mixed with asubstance that is completely non-toxic such that the mixture is ½EG, theacute oral (rat) LD₅₀ value of the mixture would be estimated to be9,400 mg/kg, or twice that of EG by itself. This is a reasonableestimate since the same quantity of the mixture would contain only ½ theamount of EG.

[0068] PG has an acute oral (rat) LD₅₀ value of 20,000 mg/kg. Asdescribed in the World Health Organization Classification of Pesticidesby Hazard and Guidelines to Classification 1998-99, the LD₅₀ of amixture containing substances having known LD₅₀ values can be estimatedby the following formula:

C _(A) /T _(A) +C _(B) /T _(B) + . . . +C _(Z) /T _(Z)=100/T _(Mxtr)

[0069] Where:

[0070] C=the % concentration of constituents A, B . . . , Z in themixture.

[0071] T=the acute oral (rat) LD₅₀ values of the constituents A, B . . ., Z.

[0072] T_(Mxtr)=the estimated acute oral (rat) LD₅₀ value of themixture.

[0073] Using the above equation, the predicted acute oral (rat) LD₅₀values of various mixtures of EG with PG and inhibitors were calculated.The results of the calculations are shown graphically in FIG. 2.

[0074] Acute oral toxicity tests were performed to determine thetoxicity of mixtures of PG and EG of the present invention. The testswere conducted by a laboratory certified by the United StatesEnvironmental Protection Agency (EPA) using standard “GLP” testprocedures as described in United States Food and Drug AdministrationRegulations, 21 C.F.R. Part 58 and EPA Good Laboratory PracticeStandards, 40 C.F.R. Part 792. As described below, the results of thistesting unexpectedly showed that the mixtures of PG and EG weresubstantially less toxic than was predicted based upon the standardtoxicity calculation for mixtures.

[0075] A formulation tested was comprised of 68.95 percent by weight EG,29.55 percent by weight PG, and corrosion inhibitors totaling 1.5percent by weight. The fraction of PG in the mixture as compared to thetotal of the polyhydric alcohols was 30 percent and the fraction of EGwas 70 percent. Referring to FIG. 2, the predicted LD₅₀ value for thisformulation is 5,762 mg/kg, which is about 23 percent greater than EG'sLD₅₀ value of 4,700 mg/kg. A range test was conducted in which the ratswere given up to maximum possible doses of approximately 21,000 mg/kg(an amount that completely filled the rats' stomachs). No rat deathswere reported, and all of the rats actually gained a significant amountof weight during the test period.

[0076] This result was completely unexpected as the toxicity of the testformulation was so low (despite the substantial concentration of EG)that it was impossible to determine an LD₅₀ value; i.e., there is noLD₅₀ value for this formulation. As PG does have an LD₅₀ value (half ofPG rats die with a dose of 20,000 mg/kg), the tested non-aqueous coolantformulated according to the invention is actually less toxic than PGitself.

[0077] A range test was performed using a formulation comprised of 95percent by weight EG and 5 percent by weight PG. Referring to FIG. 3,the predicted LD₅₀ value of this formulation is 4,904 mg/kg, only 4percent greater than EG's LD₅₀ value of 4,700 mg/kg. In the range testthere were no mortalities at 5,000 and 10,000 mg/kg doses, all of therats died at 20,000 and 25,000 mg/kg doses and one of the two rats diedat the 15,000 gm/kg dose level. The test performed indicates that theLD₅₀ value is somewhere near 15,000 mg/kg, a value that demonstratesthat the fluid is of very low toxicity.

[0078] The results of the toxicity tests of the EG and PG mixtures wereas astounding as they were unexpected. Without being limited to anyparticular theory, the inventors currently believe that PG is an ADHenzyme inhibitor. By incorporating PG into an EG formulation, it appearsthat the conversion of EG into glycoaldehyde is significantly reduced orprevented altogether from the time of ingestion. Without the formationof glycoaldehyde, the further toxic metabolites of glycolic acid,glyoxylic acid, and oxalic acid are not created. Acidosis, precipitationof calcium oxylate crystals, hypocalcemia, renal failure, and all theother characteristics of EG poisoning do not occur. The inhibitionprovided by the PG remains until the EG is expelled from the body.

[0079] The significance of the discovery that even small amounts of PGmixed with EG render the mixture non-hazardous is that much largerpercentages of EG than heretofore thought prudent can be incorporatedinto PG and EG non-aqueous coolants without causing toxicity problems.

[0080] Limit tests at 5,000 mg/kg were performed on mixtures where thePG and EG percentages of total polyhydric alcohols were 10%/90%, 5%/95%,4%/96%, 3%/97%, 2%/98%, and 1%/99%. In every case, no rats died. Recallthat the LD₅₀ value for EG itself is 4,700 mg/kg, indicating that atthat dosage half of test rats die. At 5,000 mg/kg doses for all of therats in the above six studies, none of the rats died. The significanceof this fact is that a non-aqueous coolant formulated with EG being 95%by weight of the total polyhydric alcohols in the coolant still has thecapacity to have EG added to it without the coolant becoming toxic.

[0081] Toxicity Testing of EG Combined with Glycerol

[0082] A limit test was performed for a mixture of glycerol and EGwherein the percentage of glycerol was 20% by weight and the percentageof EG was 80% by weight. Referring to FIG. 4, the predicted LD₅₀ valuefor this formulation is 5,374 mg/kg, or 14 percent greater than EG'sLD₅₀ value of 4,700 mg/kg. The limit test was performed at a dosage of8,000 mg/kg. One rat died but that rat appeared to be anomalous as allof the remaining 9 rats survived, experiencing weight gains of between21% and 53% over the two-week test period.

[0083] A range test was performed using a formulation comprised of 95percent by weight EG and 5 percent by weight glycerol. Referring to FIG.4, the predicted LD₅₀ value of this formulation is 4,852 mg/kg, only 3percent greater than EG's LD₅₀ value of 4,700 mg/kg. In the range testthere were no mortalities at 5,000 and 10,000 mg/kg doses, all of therats died at 20,000 and 25,000 mg/kg doses, and one of the two rats diedat the 15,000 gm/kg dose level (exactly the same result as the similartest using 95% EG and 5% PG). The test performed indicates that the LD₅₀value for the 95%/5% EG/glycerol mixture is somewhere near 15,000 mg/kg,a value that demonstrates that the fluid is of very low toxicity. Thusit was discovered that glycerol renders mixtures of EG that containglycerol, even in small concentrations, very low in toxicity. Theinventors currently believe that glycerol is as effective as PG inacting as an ADH enzyme inhibitor.

[0084] Glycerol, a polyhydric alcohol with three hydroxyl groups(boiling point 554° F., 290° C.), is not considered by the inventors tobe superior to PG as a heat transfer fluid ingredient, however. Glycerolis, for example, more costly and more viscous than PG and has a freezingpoint that is too high for low temperature applications. It can,however, be satisfactorily used in concentrations of from 1% to 10% ofthe weight of the EG plus glycerol in a heat transfer fluid for toxicityreduction in situations where low temperatures are not encountered.Glycerol can also be mixed with PG and the mixture blended with EG. Formost applications mixtures of EG with PG would be preferred to mixturesof EG with glycerol.

[0085] Whether EG is blended with PG or glycerol, the mixture willremain “safe” in all stored, or in use conditions, due to the highsaturation temperatures and low vapor pressures of EG, PG, and glycerolbase fluids. Fluid entering the environment from draining or from leaksor other unintentional discharges from an engine cooling system using acoolant according to this invention will retain the approximate ratio ofthe polyhydric alcohols in the blended concentrate and will thereby beessentially non-hazardous to the environment. In addition, if EG wereinadvertently added to a non-aqueous heat transfer fluid of the presentinvention, the resulting mixture would be reduced in toxicity, from theEG added, far beyond the reduction predicted by dilution alone and wouldmost likely be essentially non-hazardous to the environment. Also, otherpolyhydric alcohols may be present, in low concentrations, in mixturesof PG or glycerol with EG without altering the essentially non-hazardouscharacteristics of the non-aqueous heat transfer fluid.

[0086] Corrosion Inhibitor Additives

[0087] The non-aqueous heat transfer fluid of the present inventionutilizes only additives that are soluble in PG and in EG, or in glyceroland EG, and thus does not require water for the additives to enter intoor remain in solution. In addition to being soluble in EG and PG or inEG and glycerol, each chosen additive is a corrosion inhibitor for oneor more specific metals that may be present in an engine. A nitratecompound, such as sodium nitrate, is utilized as an additive to inhibitcorrosion for iron or alloys containing iron, such as cast iron.Although the primary function of sodium nitrate is to prevent corrosionof iron, it also slightly inhibits solder and aluminum corrosion. Anazole compound, such as tolyltriazole, functions as acorrosion-inhibiting additive for both copper and brass. A molybdatecompound, such as sodium molybdate, primarily functions as a corrosioninhibitor for lead (from solder), but is also beneficial in decreasingcorrosion for many other metals. Notably, there is no need for nitritesin any formulation of the non-aqueous heat transfer fluid.

[0088] The choice of PG, and EG-soluble additives thus depends on whichmetals are of concern with regard to corrosion of metal surfaces.Typically, sodium nitrate, tolyltriazole and sodium molybdate would beadded to formulate a universally usable heat transfer fluid becauseiron, solder, aluminum, copper and/or brass are often used in enginecooling system components. However, an additive could be reduced oreliminated if the particular metal it acts on is eliminated. Forexample, if lead-based solder is eliminated, then the content of sodiummolybdate could be reduced, or it might not be required at all.

[0089] The corrosion inhibitor additives may be present in a range froma concentration of about 0.05% by weight to about 5.0% by weight of theformulated heat transfer fluid, and are preferably present at aconcentration of less than 3.0% by weight. Solutions below about 0.1% byweight are not as effective for long life inhibition, while solutionsover about 5.0% may result in precipitation of the additive. In apreferred embodiment, each corrosion inhibitor additive is present in aconcentration of about 0.3% to about 0.5% by weight depending upon theservice life of the coolant. Another advantage of the present inventionis that light alloys will have little or no corrosion in PG or PG and EGnon-aqueous fluids. Accordingly, metals such as magnesium and aluminumwill exhibit little or no corrosion, and additives to limit corrosion ofthese metals can be eliminated.

[0090] The use of sodium nitrate, tolyltriazole and sodium molybdate ascorrosion inhibitor additives has many advantages. For example, theseadditives are not rapidly depleted in service, and therefore the enginecoolant may be formulated to last for heretofore unobtainable serviceperiods, without change or additive replenishment, of up to about 10,000hours or 400,000 miles (643,720 km) in many forms of engines andvehicles. Another advantage of these PG or PG and EG soluble additivesis that the additives go into solution or suspension readily and remainin solution or suspension, even in extreme concentrations. Theseadditives will not precipitate from the solutions even when eachadditive is present in concentrations of up to 5.0 percent by weight.Moreover, these additives will not degrade significantly as a result ofinteractions with each other, the additives are not abrasive, and theadditives and coolant protect all metals, including magnesium, for thesame operating period.

[0091] The non-aqueous PG or PG and EG soluble additives of the presentinvention do not become depleted over extended hourly usage or mileageand thus the need for supplemental coolant additives is ordinarilyeliminated. Nevertheless, if it should become desirable to addsupplemental coolant additives, the non-aqueous formulation exhibitsadvantages because the supplemental coolant additives will more readilyenter stable solution or suspension with the present invention than inaqueous coolants. Moreover, the proper balance of supplemental coolantadditives is easier to maintain, with a broad possible range ofconcentrations from about 0.05% by weight to about 5.0% by weight.

[0092] Should the supplemental addition of additives be required, thesupplements may be added in either dry powder form, or as a dissolvedconcentrate directly to the cooling system. The supplements may be addedto a cool engine (50° F. or above) and will dissolve into solutionmerely by idling the engine, without clogging the radiator or heatercores. Also, because the preferred target base solution for eachadditive is about 0.5% by weight and the saturated limit is about 5.0%,there is little chance of inadvertent addition of an unacceptable amountof supplemental additive. By contrast, current water-based additivesmust be added to a hot coolant, then run hard (to enter solution) andare easily oversaturated, which can cause radiator and heater damage.

[0093] As used herein and in the claims, “non-aqueous” means that wateris present only as an impurity in the non-aqueous heat transfer fluidpreferably, in no greater than a starting concentration of about 0.5% byweight. Most preferably, the non-aqueous heat transfer fluid containsvirtually no water. Although an increase in water is not desired duringuse, the present invention can accommodate the presence of some water.Because PG is a hygroscopic substance, water can enter the coolant fromthe atmosphere, or water can escape from the combustion chamber into thecoolant from a combustion gasket leak into the cooling chamber. Althoughthe essence of the invention is to avoid water, the invention willpermit some water as an impurity; however, the water fraction of thecoolant in use is preferably restricted to below about 5.0% by weight,and more preferably, to below about 3.0% by weight. Further, theinvention and related cooling systems can tolerate water, fromabsorption during use, up to a maximum concentration of about 10% byweight and retain reasonably acceptable operating characteristics.

[0094] Because the heat transfer fluid of the present invention does notcontain substantial amounts of water, several of the problems associatedwith aqueous heat transfer fluids are eliminated. For example, aqueouscoolants can form violent vapor bubbles (cavitation) in the coolingsystem leading to lead and copper erosion from the effects of thevapor/gases and the reaction of water with the metals. Because thepresent invention is non-aqueous in nature, coolant vapor bubbles aresubstantially minimized and water vapor bubbles are essentiallyeliminated, thereby reducing the quantity of heavy metal precipitates inthe coolant.

[0095] In conventional water-based coolants, acidity of the coolant is aconcern. If the coolant is acidic, corrosion of metal surfaces may beincreased. To avoid acidic conditions, conventional water-based coolantsrequire buffering agents to make the coolant more basic (an increase inthe pH to 10 to 14). At least about 5% of the content of conventionalantifreeze concentrates must be water in order to dissolve these buffers(e.g. phosphates, borates, carbonates, and the like). The non-aqueousheat transfer fluid of the present invention does not require bufferingbecause acid anhydrides that are present would require the presence ofwater to form acids. Without the water, the non-aqueous coolant does notbecome corrosive and no buffers are needed.

[0096] A preferred embodiment of the non-aqueous heat transfer fluid iscompared to the formulation of a conventional coolant below: B.Conventional Coolant A. Preferred (EG Antifreeze Components: EmbodimentConcentrate Plus Water)  1) Polyhydric Alcohol a. PG or PG/EG Mixturewt. % >98.4    b. Ethylene Glycol wt. % — 46.75  2) Water wt. % <0.1  50.83  3) Tolyltriazole wt. % 0.5  0.10  4) Sodium Nitrate wt. % 0.5 0.05  5) Sodium Molybdate wt. % 0.5  0.05  6) Sodium Metaborate wt. % — 0.50  7) Sodium Hydroxide wt. % —  0.12  8) Sodium Benzoate wt. % — 1.50  9) Sodium Nitrite wt. % —  0.05 10) Sodium Metasilicate wt. % — 0.10

[0097] The respective percentage weights of PG and EG in the PG/EGmixture are normally set for the smallest proportion of PG that willachieve the freezing point protection required; see FIG. 1. For afreezing point of −35° F. (−37.2° C.), for example, the percentage of PGin the mixture of the polyhydric alcohols is 30 percent (by weight) andthat for EG is 70 percent. As the total percentage by weight of themixture is >98.4%, the percentage of the fully formulated coolant, byweight, that is PG would be 29.5%. The figure for the EG would be 68.9%.The remainder of the formulation is corrosion inhibitors and possibly atrace amount of water present only as an impurity.

[0098] Corrosion Testing Using Embodiments of the Invention

EXAMPLE 1

[0099] This corrosion test was performed using the test procedure setforth in ASTM #D-1384 (Modified). Six specimens, typical of metalspresent in an engine coolant system, were totally immersed in the testcoolants contained in glassware. Coolant “A” was a non-aqueous heattransfer fluid of the present invention in which the polyhydric alcoholportion was 100 percent PG. Coolant “B” was a conventional enginecoolant formulation comprised of an EG based antifreeze concentratemixed with water.

[0100] In the ASTM test procedure, the coolant is aerated by bubblingair up through the glassware, and maintained at a test temperature of190° F. (88° C.) for 336 hours. This procedure was modified to moreaccurately reflect the conditions that would be experienced by themetals in an engine coolant system in use. The tests were conducted at acontrol temperature of 215° F. (101.6° C.) to simulate severe duty use.Coolant “A” was tested without aeration being applied in order to moreclosely approximate its operation in a non-aqueous engine coolingsystem, such as, for example, the engine cooling system described inU.S. Pat. Nos. 4,550,694; 4,630,572; and 5,031,579; 5,381,762;5,385,123; 5,419,287; 5,868,105 and 6,053,132. The conventionalantifreeze composition in Coolant “B” was aerated in the normal mannerof the ASTM #D-1384 test. At the completion of the test, corrosion wasmeasured by weight loss of each metal specimen. The results of the testwere as follows:

[0101] 1) Light Alloy Engines—Aluminum or Magnesium Head and Block Δ WT(mg) Δ WT (mg) METAL COOLANT “A” COOLANT “B” ASTM STD. Magnesium−1.3 >−1,000 −50 Aluminum +0.3 −21.1 −30 Steel −0.5 −3.9 −10 Copper −3.7−7.4 −10 Solder −9.0 −19.2 −30 Brass −0.6 −5.1 −10

[0102] 2) Combined Alloy Engines—Aluminum [partial] with iron, or alliron Δ WT (mg) Δ WT (mg) METAL COOLANT “A” COOLANT “B” ASTM STD. CastIron +1.0 −6.2 −10 Aluminum +2.0 −18.6 −30 Steel 0.0 −4.3 −10 Copper−3.0 −8.9 −10 Solder −6.1 −19.7 −30 Brass 0.0 −4.7 −10

[0103] The results with a positive gain in weight occur because ofplating out of transients from the other specimens used in the test, andthose metals that gained the transient weight virtually did not lose anyweight due to corrosion themselves.

EXAMPLE 2

[0104] This corrosion test was conducted to determine the amount ofcorrosion of cast aluminum or magnesium alloys in engine coolants underheat rejecting conditions. A cast aluminum alloy specimen, typical ofthat used for engine cylinder heads or blocks, was exposed to testengine coolant solutions. Coolant “A” was a non-aqueous coolant of thepresent invention with 100 percent PG. To simulate the operatingconditions of a coolant system using a non-aqueous coolant, the testusing Coolant “A” was conducted at a temperature of 275° F. (135° C.)and a pressure of 2 psig (13.79 kPa), which is slightly above ambientpressure. Test Coolant “B” contained an ASTM prescribed corrosive waterused to make up the water fraction of a 50/50 EG/water coolant. The testconditions for Coolant B, which simulate the conditions in an aqueouscoolant engine cooling system, were a temperature of 275° F. (135° C.)and a pressure of 28 psig (193 kPa).

[0105] In each test, a heat flux was established through the specimen,and the test specimens were maintained under the test conditions for 168hours (one week). The corrosion of the test specimens was measured bythe weight change of the specimen in milligrams. The test provided anevaluation of the coolant solution's ability to inhibit aluminum, aswell as magnesium, corrosion at a heat-rejecting surface. The results ofthis test were as follows: Δ WT (mg) Δ WT (mg) METAL COOLANT “A” COOLANT“B” ASTM STD. Aluminum  0.067 1.61 <2 Magnesium 0.18 5.79 <2

EXAMPLE 3 Field Test

[0106] A 3.8L V-6 engine was operated over the road for a test period of55,000 miles (88,511.5 km). The engine cooling system in the vehicle wasconfigured as described in U.S. Pat. No. 5,031,579. Coolant “A” wasidentical to the non-aqueous coolant described in Example 1 above. Therewas no draining or replacing of the coolant during the test period. Ametal specimen bundle was placed within the full flow of the enginecoolant stream (lower hose) and was kept submerged in the coolant at alltimes. Performance of the test coolant's ability to inhibit metalcorrosion was evaluated by comparing the results in milligrams lost ofthe specimen at the end of the test period to ASTM test standards. Theresults were as follows: Δ WT (mg) METAL COOLANT “A” ASTM STD. Cast Iron−2.8 −10 Aluminum +0.2 −30 Steel −1.1 −10 Copper −1.3 −10 Solder −3.7−30 Brass −0.9 −10 pH at start +7.1 NA pH at finish +6.9 NA

[0107] Method of Manufacture

[0108] The non-aqueous heat transfer fluid of the present invention maybe manufactured by the methods described below. The non-aqueous heattransfer fluid may be made in a batch process. Initially, calculationsmust be performed to determine the required quantity for theingredients. For example, the following calculations would be performedto determine the quantity of each ingredient to mix 6,500 gallons ofnon-aqueous heat transfer fluid:

[0109] 1. Determine the approximate weight of 6,500 gallons of the finalproduct.

[0110] a. From the desired percentage (by weight) of PG (%_(PG)) in thepolyhydric alcohol portion of the formulated coolant (a figure in therange of 1% to 100%), compute the density (lbs. per gallon) of the mixedpolyhydric alcohols according to the following formula:D_(mixed PA)=100/((%_(PG)/8.637)+((100-%_(PG))/9.281))

[0111] b. The estimated weight in pounds for 6,500 gallons:

[0112] EStWt₆₅₀₀=D_(mixed PA)×6,500

[0113] 2. Compute the weights for each component of the non-aqueous heattransfer fluid to be added to the batch:

[0114] a. Each of the three additives is 0.5 percent of the totalweight.

[0115] 1. The tolyltriazole will weigh 0.005×EStWt₆₅₀₀.

[0116] 2. The sodium nitrate will weigh 0.005×EStWt₆₅₀₀.

[0117] 3. The sodium molybdate will weigh 0.005×EStWt₆₅₀₀.

[0118] b. The weight of the total polyhydric alcohols (Wt_(TotPA)) willbe (1−0.015)×EstWt₆₅₀₀.

[0119] c. The PG will weigh %_(PG)×WtTotPA/100 lbs.

[0120] d. The EG will weigh (100−%_(PG))×Wt_(TotPA)/100 lbs.

[0121] After the quantity of each component has been calculated, thenon-aqueous heat transfer fluid may be mixed together using a variety ofmethods. For example, the additives may be pre-mixed with a portion ofthe polyhydric alcohol(s) that will be used in the main body of thenon-aqueous heat transfer fluid. In one embodiment of the presentinvention in which the polyhydric alcohol portion of the coolant isentirely PG and the quantity to be produced is 6,500 gallons, thismethod would be performed using at least the following steps:

[0122] 1. Provide 3,300 lbs. of industrial grade PG in an additive tankand add the following inhibitors: a. tolyltriazole 281 lbs. b. sodiumnitrate 281 lbs. c. sodium molybdate 281 lbs.

[0123] 2. Blend for 20 min at a room temperature of 60° to 70° F. usinga standard paddle or propeller, or air agitation.

[0124] 3. Provide 52,000 lbs. of industrial grade PG in a 6,500 gallonor larger main tank.

[0125] 4. Add the contents of the additive tank to the main tank.

[0126] 5. Blend the contents of the main tank for 30 min at a roomtemperature of 60° to 70° F. using a standard paddle or propeller, orair agitation.

[0127] In an embodiment of the invention in which the heat transferfluid is comprised of 30 percent PG by weight and 70 percent EG byweight, the method of manufacturing the heat transfer fluid bypre-mixing additives with a polyhydric alcohol may be as follows:

[0128] 1. Provide 3,300 lbs. of industrial grade EG in an empty additivetank and add the following inhibitors: a. tolyltriazole 295 lbs. b.sodium nitrate 295 lbs. c. sodium molybdate 295 lbs.

[0129] 2. Blend for 20 min at a room temperature of 60° to 70° F. usinga standard paddle or propeller, or air agitation.

[0130] 3. Provide 17,435 lbs. of industrial grade PG in an empty 6,500gallon or larger main tank.

[0131] 4. Add 37,385 lbs. of industrial grade EG to the main tank.

[0132] 5. Add the contents of the additive tank to the main tank.

[0133] 6. Blend the contents of the main tank for 30 minutes at a roomtemperature of 60° to 70° F. using a standard paddle or propeller, orair agitation.

[0134] In an another method for producing the heat transfer fluid, theadditives may be mixed directly into the polyhydric alcohol(s), and thepre-mixing steps may be eliminated. For a heat transfer fluid comprisedof 100 percent PG, this method of is performed using at least thefollowing steps:

[0135] 1. Provide 55,300 lbs. of industrial grade PG in a 6,500 gallonor larger main tank and add the following inhibitors: a. tolyltriazole281 lbs. b. sodium nitrate 281 lbs. c. sodium molybdate 281 lbs.

[0136] 2. Blend for 1.5 hours at a room temperature of 60° to 70° F.using a standard paddle or propeller, or air agitation.

[0137] This method may also be used to produce heat transfer fluidscomprised of mixtures of PG and EG. For example, for a heat transferfluid comprised of 30 percent PG by weight and 70 percent EG by weight,at least the following steps would be performed:

[0138] 1. Provide 17,435 lbs. of industrial grade PG in an empty 6,500gallon or larger main tank.

[0139] 2. Add 40,685 lbs. of industrial grade EG to the main tank.

[0140] 3. Add the following inhibitors to the main tank: a.tolyltriazole 295 lbs. b. sodium nitrate 295 lbs. c. sodium molybdate295 lbs.

[0141] 4. Blend for 1.5 hours at a room temperature of 60° to 70° F.using a standard paddle or propeller, or air agitation.

[0142] Either of the methods described above will result in a stablefully-formulated non-aqueous heat transfer fluid in a period of timethat may be as little as ⅙ of the time typically required to properlyformulate conventional EG or PG antifreeze coolant concentrates.

[0143] In a further embodiment of the present invention, a preparationfluid for the absorption of water from heat exchange systems is providedthat is especially useful when converting from a water-based heattransfer fluid to a heat transfer fluid of the present invention. Thepreparation fluid is installed in a heat exchange system temporarily anddrained prior to installation of the non-aqueous heat transfer fluiddescribed above. The preparation fluid is comprised of EG and apolyhydric alcohol that acts as an ADH enzyme inhibitor, preferablyPG,to reduce the toxicity of the EG. As the preparation fluid is used inthe heat exchange system only temporarily, corrosion inhibitorstypically are not required, although corrosion inhibitors may beincluded if desired. The preparation fluid absorbs water from the heatexchange system. The preparation fluid may be used for multipleapplications until it has become saturated with water, at which time itis disposed of or recycled to remove the absorbed water. Theconcentration of PG in the preparation fluid is typically between about1% to about 50% of the total weight of EG and PG in the fluid. In apreferred embodiment, the concentration of PG is about 5% of the totalweight of EG and PG in the fluid.

[0144] As will be recognized by those of ordinary skill in the art basedon the teachings herein, numerous changes and modifications may be madeto the above-described embodiments of the present invention withoutdeparting from its spirit or scope. Accordingly, the detaileddescription of preferred embodiments is to be taken in an illustrativerather than a limiting sense.

We claim:
 1. A polyhydric alcohol based heat transfer fluid for use in aheat exchange system, said heat transfer fluid comprising: (a) a firstpolyhydric alcohol consisting of ethylene glycol; (b) at least onesecond polyhydric alcohol, wherein the second polyhydric alcohol acts asan alcohol dehydrogenase enzyme inhibitor and, wherein the secondpolyhydric alcohol has a boiling point above approximately 150° C.; and(c) at least one corrosion inhibitor additive that is soluble in thefirst and second polyhydric alcohols.
 2. The heat transfer fluid ofclaim 1, wherein the corrosion inhibitor additive is selected from thegroup consisting of a molybdate salt, a nitrate salt and an azole. 3.The heat transfer fluid of claim 1, wherein the polyhydric alcoholscomprise from about 85 percent by weight to about 99.85 percent byweight of the heat transfer fluid.
 4. The heat transfer fluid of claim1, wherein the second polyhydric alcohol is propylene glycol.
 5. Theheat transfer fluid of claim 4, wherein ethylene glycol comprises fromabout 0 percent by weight to about 99 percent by total weight of thetotal weight of the polyhydric alcohols, and propylene glycol comprisesfrom about 1 percent by weight to about 100 percent by weight of thetotal weight of the polyhydric alcohols.
 6. The heat transfer fluid ofclaim 1, wherein the second polyhydric alcohol is glycerol.
 7. The heattransfer fluid of claim 6, wherein ethylene glycol comprises from about90 percent by weight to about 99 percent by total weight of the totalweight of the polyhydric alcohols, and glycerol comprises from about 1percent by weight to about 10 percent by weight of the total weight ofthe polyhydric alcohols.
 8. The heat transfer fluid of claim 1, whereinthe corrosion inhibitor is comprised of a molybdate salt in aconcentration of between about 0.05 percent to about 5 percent by weightof the total weight of the heat transfer fluid.
 9. The heat transferfluid of claim 1, wherein the corrosion inhibitor is comprised of anitrate salt in a concentration of between about 0.05 percent to about 5percent by weight of the total weight of the total weight of the heattransfer fluid.
 10. The heat transfer fluid of claim 1, wherein thecorrosion inhibitor is comprised of an azole in a concentration ofbetween about 0.05 percent to about 5 percent by weight of the totalweight of the heat transfer fluid.
 11. The heat transfer fluid of claim8, wherein the molybdate salt is sodium molybdate.
 12. The heat transferfluid of claim 9, wherein the nitrate salt is sodium nitrate.
 13. Theheat transfer fluid of claim 10, wherein the azole is tolyltriazole. 14.The heat transfer fluid of claim 1, wherein the corrosion inhibitor iscomprised of at least one of (i) sodium molybdate in a concentrationbetween about 0.05 percent by weight to about 5 percent by weight of thetotal weight of the heat transfer fluid, (ii) sodium nitrate in aconcentration between about 0.05 percent by weight to about 5 percent byweight of the total weight of the heat transfer fluid, or (iii)tolyltriazole in a concentration between about 0.05 percent by weight toabout 5 percent by weight of the total weight of the heat transferfluid.
 15. The heat transfer fluid of claim 1, wherein (a) ethyleneglycol comprises about 70 percent by weight of the total weight ofpolyhydric alcohols in the heat transfer fluid; (b) propylene glycolcomprises about 30 percent by weight of the total weight of polyhydricalcohols in the heat transfer fluid; (c) sodium molybdate comprisesabout 0.5 percent by weight of the total weight of the heat transferfluid; (d) sodium nitrate comprises about 0.5 percent by weight of thetotal weight of the heat transfer fluid; and (e) tolyltriazole comprisesabout 0.5 percent by weight of the total weight of the heat transferfluid.
 16. A heat transfer fluid for use in a heat exchange systemcomprising at least one polyhydric alcohol having a boiling point aboveapproximately 150° C. and means for providing a polyhydric alcohol thatacts as an alcohol dehydrogenase enzyme inhibitor.
 17. The heat transferfluid of claim 16, wherein the polyhydric alcohol that acts as analcohol dehydrogenase enzyme inhibitor is propylene glycol.
 18. The heattransfer fluid of claim 16, wherein the polyhydric alcohol that acts asan alcohol dehydrogenase enzyme inhibitor is glycerol.
 19. The heattransfer fluid of claim 16, further comprising at least one corrosioninhibitor additive that is soluble in ethylene glycol and in thepolyhydric alcohol that acts as an alcohol dehydrogenase enzymeinhibitor.
 20. The heat transfer fluid of claim 19, wherein thecorrosion inhibitor additive is selected from the group consisting of amolybdate salt, a nitrate salt and an azole.
 21. The heat transfer fluidof claim 19, wherein the polyhydric alcohols comprise from about 85percent by weight to about 99.85 percent by weight of the heat transferfluid.
 22. The heat transfer fluid of claim 19, wherein the corrosioninhibitor is comprised of a molybdate salt in a concentration of betweenabout 0.05 percent to about 5 percent by weight of the total weight ofthe heat transfer fluid.
 23. The heat transfer fluid of claim 19,wherein the corrosion inhibitor is comprised of a nitrate salt in aconcentration of between about 0.05 percent to about 5 percent by weightof the total weight of the total weight of the heat transfer fluid. 24.The heat transfer fluid of claim 19, wherein the corrosion inhibitor iscomprised of an azole in a concentration of between about 0.05 percentto about 5 percent by weight of the total weight of the heat transferfluid.
 25. The heat transfer fluid of claim 22, wherein the molybdatesalt is sodium molybdate.
 26. The heat transfer fluid of claim 23,wherein the nitrate salt is sodium nitrate.
 27. The heat transfer fluidof claim 24, wherein the azole is tolyltriazole.
 28. The heat transferfluid of claim 19, wherein the corrosion inhibitor is comprised of atleast one of (i) sodium molybdate in a concentration between about 0.05percent by weight to about 5 percent by weight of the total weight ofthe heat transfer fluid, (ii) sodium nitrate in a concentration betweenabout 0.05 percent by weight to about 5 percent by weight of the totalweight of the heat transfer fluid, or (iii) tolyltriazole in aconcentration between about 0.05 percent by weight to about 5 percent byweight of the total weight of the heat transfer fluid.
 29. The heattransfer fluid of claim 16, wherein at least one polyhydric alcohol isethylene glycol.
 30. A method for reducing the toxicity of an ethyleneglycol based heat transfer fluid comprising the steps of: (a) providingan ethylene glycol based heat transfer fluid; and (b) adding asufficient amount of a polyhydric alcohol that acts as an ADH enzymeinhibitor to reduce the toxicity of the heat transfer fluid.
 31. Themethod of claim 30, wherein the polyhydric alcohol that acts as an ADHenzyme inhibitor comprises at least about 1 percent by weight of theethylene glycol in the heat transfer fluid.
 32. The method of claim 30,wherein the polyhydric alcohol that acts as an ADH enzyme inhibitor ispropylene glycol.
 33. The method of claim 30, wherein the polyhydricalcohol that acts as an ADH enzyme inhibitor is glycerol.
 34. A fluidfor use in absorbing water from a heat exchange system comprising: (a) afirst polyhydric alcohol consisting of ethylene glycol; and (b) a secondpolyhydric alcohol, wherein the second polyhydric alcohol acts as analcohol dehydrogenase enzyme inhibitor.
 35. The fluid of claim 34,wherein the second polyhydric alcohol is propylene glycol.
 36. The fluidof claim 35, wherein the propylene glycol comprises from about 1 percentto about 50 percent by weight of the total weight of ethylene glycol andpropylene glycol.
 37. The fluid of claim 35, wherein the propyleneglycol comprises about 5 percent by weight of the total weight of theethylene glycol and propylene glycol.
 38. The fluid of claim 34, whereinthe second polyhydric alcohol is glycerol.
 39. The fluid of claim 38,wherein the glycerol comprises about 5 percent by weight of the totalweight of ethylene glycol and glycerol.